Counterweight requirements for C8 Edge HD

Hi there everyone, just received delivery of my C8 Edge HD, which will reside on my Vixen SXW EQ. The mount was delivered with just a single 1.9Kg counterweight. I suspected that this would not be sufficient for the 'Edge' and had my suspicions confirmed when I attempted a little balancing exercise earlier today. I imagine that I should only need one additional counterweight, for visual work, however I was wondering if anybody on CN has experience with this combination, and could provide some insight into counterweight requirement for prime focus AP with a DSLR on this outfit.

I have a Meade 8-inch LX200 SCT OTA (a little heavier than the Celestron 8-inch Edge) that I use on my Vixen SXW mount and it's perfectly balanced with only one Vixen SX 8.1 lbs. counterweight at the end of the counterweight bar (with margin left for adjustment).